Spatiotemporal organization of cryptic North American Culex species along an urbanization gradient

Landscape heterogeneity creates diverse habitat and resources for mosquito vectors of disease. A consequence may be varied distribution and abundance of vector species over space and time dependent on niche requirements. We tested the hypothesis that landscape heterogeneity driven by urbanization influences the distribution and relative abundance of Culex pipiens , Cx. restuans, and Cx. quinquefasciatus, three vectors of West Nile virus (WNv) in the eastern North American landscape. We collected 9,803 cryptic Culex from urban, suburban, and rural sites in metropolitan Washington, District of Columbia, during the months of June-October, 2019-2021. In 2021, we also collected mosquitoes in April and May to measure early-season abundance and distribution. Molecular techniques were used to identify a subset of collected Culex to species (n = 2,461). Ecological correlates of the spatiotemporal distribution of these cryptic Culex were examined using constrained and unconstrained ordination.

Seasonality was not associated with Culex community composition in June-October over three years but introducing April and May data revealed seasonal shifts in community composition in the final year of our study. Culex pipiens were dominant across site types, while Cx. quinquefasciatus were associated with urban environments, and Cx. restuans were associated with rural and suburban sites. All three species rarely coexisted.

Synthesis and applications: Our work demonstrates that human-mediated land-use changes influence the distribution and relative abundance of Culex vectors of WNv, even on fine geospatial scales. Site classification, percent impervious surface, distance to city center, and longitude predicted Culex community composition. We documented active Culex months before vector surveillance typically commences in this region, with Culex restuans being most abundant during April and May. Active suppression of Cx. restuans in April and May could reduce early enzootic transmission, delay the seasonal spread of WNv, and thereby reduce overall WNv burden. By June, the highest risk of epizootic spillover of WNv to human hosts may be in suburban areas with high human population density and mixed Culex  assemblages that can transmit WNv between birds and humans. Focusing management efforts there may further reduce human disease burden.